1. Technical Field
The present invention relates to an optical disk drive, and more particularly to reproduction processing performed when a defect is present in an optical disk.
2. Related Art
A reproduction rate of an optical disk is appropriately optimized according to a reproducing state. For instance, when data are reproduced by means of; for example, equipment incorporated in or connected to a personal computer, the data must be reproduced as fast as possible, and hence a reproduction rate is increased. Further, at the time of playback of a video or music, a transfer rate is determined. Therefore, a reproduction rate which is faster than the predetermined transfer rate is not required. Even if the data can be reproduced at high speed, the reproduction rate is maintained at a low rate in consideration of tranquility.
In the meantime, when side-to-side runout or mass eccentricity is present in an optical disk or when meandering of a track, or the like, is present, data cannot be read when reproduction is performed at a high rate, thereby resulting in occurrence of an error. In consideration of this, decreasing the reproduction rate has been proposed.
JP 10-40640 A discloses that, when excessive vibrations arise in the middle of a disk being subjected to high-speed reproduction or when mass eccentricity of a predetermined amount or greater is detected, the rotational speed of the disk is decreased to perform reproduction at a low rate, thereby diminishing vibrations.
JP 2002-251844 A discloses that, when a poorly-readable area, such as a defect, is detected, data recorded in the poorly-readable area are read without decreasing the rotational speed of the optical disk by means of switching a cutoff frequency of a high-pass filter.
JP 2003-297007 A discloses that the rotational speed of a disk is set to the minimum rotational speed when reproduction of the disk is started and that control is performed so as to increase the rotational speed of the disk stepwise until a read error arises, whereby, when compared-with a case where the rotational speed is decreased from the maximum rotational speed, a time elapsed before reproduction is shortened.
JP 2004-281041 A discloses that, when data are recorded/reproduced in or from an optical disk that rotates at predetermined equiangular velocity, occurrence of an error during recording/reproduction of data is monitored and that, when occurrence of an error during recording/reproduction of data is detected, the rotational speed of the optical disk is controlled so as to come to equiangular velocity which is lower than the predetermined equiangular velocity, thereby shortening a time required to record/reproduce data.
In any of the related-art techniques, when a read area of defects is detected, the rotational speed of the disk is indiscriminately decreased as compared with a case where the read area of defects is not detected. However, the present applicant found that, under such a control method for indiscriminately decreasing rotational speed, data cannot be read depending on the nature of defects in the optical disk. For example, when flaws or stains are present in an optical disk, a read error arises. However, it is found that, even when the rotational speed of the optical disk is decreased as a result of occurrence of a read error, data still remain unreadable and, rather, data-reading performance is degraded.